Playing a game tonight on the Opt in 5.2 Beta, with a custom race:
In box space battles I had the Battle viewer showed a blank screen through out, (though still showed the hud) the battle played out but with no visuals. Tried the replay exactly the same no visuals no matter what camera angle I went too.
The custom race was not a Mod by the way just a custom race I created in game the standard way. The battle viewer was working when I played Humans in Beta 5.1.